1. Field of the Invention
The present invention relates to a high density optical disc, and more particularly, to an optical disc having address information recorded thereon so as to access the information in small units, and an address information modulation method thereof.
2. Description of the Related Art
Currently, optical discs having a high recording density and a high accessing speed are being developed to meet the computer and consumer electronics needs. Generally, desired specifications of a high density (HD) digital versatile disc (DVD) having a capacity of 23 GB or more and using a blue laser beam, include a 405 nm wavelength, a 0.85 numerical aperture (NA), a 12 cm diameter, and a 0.1 mm cover layer thickness. In the HD DVD, development trends show that an error correction unit may increase to 64 KB to increase an error correction capability thereof. In addition, in a next-generation optical disc recording/reproducing apparatus having a capacity of 23 GB or more and using a blue laser beam, a minimum shift keying (MSK) modulation method or a harmonic modulated wave (HMW) modulation method is available as a method to form tracks on a disc. That is, using the MSK or HMW modulation method, physical address information for accessing the disc is modulated into a wobble signal, and tracks are formed on the disc. Accordingly, the disc can be accessed using the address information obtained by demodulating the wobble signal reproduced from a track signal.
FIG. 1 illustrates a conventional method of forming address information and additional information in tracks on a disc. As shown in FIG. 1, physical address information 11, for accessing the disc, and other additional information 12 are modulated together 13 by a predetermined modulation method 14, and the modulated signal is formed in a track on the disc 15. Here, the modulation method may be an MSK or HMW modulation method. According to information contents of the address information or other additional information, a carrier signal is MSK or HMW modulated, and the modulated carrier signal is formed in a track on the disc. The track on the disc has the same shape as the modulated carrier signal and is referred to as a wobble signal.
However, the information contents of the address information or other additional information are MSK or HMW modulated in units of 1 bit into a predetermined number of carrier signals, and the modulated carrier signals are formed in tracks on the disc. To read this information from the disc, an MSK or HMW demodulation is performed using a predetermined number of wobble signals such that 1-bit-long address information or other information is obtained. Thus, according to the related art, 1-bit address information or other additional information is expressed by a predetermined number of wobble or carrier signals, and therefore, a physical address unit of the disc becomes large. Accordingly, the related art method may not be appropriate, for example, for a small-sized disc for mobile communications. Also, where a defect occurs in a small-sized disc utilizing the method above, the same loss as the size of an access unit occurs. Therefore, the smaller the size of an access unit, the more advantageous the access unit.